Flat hollow brushless servo motor with tool mounting hole

ABSTRACT

A flat, hollow brushless servomotor ( 1 ) has a motor housing ( 2 ), housing through holes ( 22   a,    23   a ) formed in a center of both end plate portions ( 22, 23 ), a rotor shaft ( 41 ) of which a portion of both ends is exposed from the through holes, a tool-mounting hole ( 43 ) that extends through a center thereof, and workpiece insertion recesses ( 24, 25 ) formed in an external surface of both end plate portions ( 22, 23 ) of the motor housing ( 2 ) by reducing the thickness thereof. A workpiece with a shape that has facing portions facing each other across a narrow space can be introduced from an outside to a center of the motor ( 1 ) along the workpiece insertion recesses, and the facing portions of the workpiece can be machined by a tool mounted in the center of the motor.

TECHNICAL FIELD

The present invention relates to an SPM-type brushless servomotor inwhich a ring magnet is used as a rotor, and particularly relates to aflat, hollow brushless servomotor whose length in an axial direction isshort, and that is provided with a tool-mounting hole.

BACKGROUND ART

An example of a hollow brushless servomotor is disclosed in the patentdocument 1 listed below. In the motor cited therein, an encoder isdisposed in a rear end portion of a motor output shaft, and a front-endportion of the hollow motor output shaft is adapted to be engaged with aload side via a reduction gear.

PATENT DOCUMENT 1: JP-U 03-54352

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

An object of the present invention is to provide a flat, hollowbrushless servomotor that is suitable for applications in which a toolis directly mounted on a rotational shaft of the motor and a workpieceis pressed from both sides thereof to carry out predetermined machining.

Means of Solving the Problems

A flat, hollow brushless motor of the present invention has:

a flattened tubular motor housing sealed at both ends;

first and second housing through holes formed in a center of first andsecond end plate portions on both sides of the motor housing;

a rotor shaft of which a portion of both ends is exposed from the firstand second housing through holes;

a tool-mounting hole that extends through a center of the rotor shaft;and

first and second workpiece insertion recesses formed in externalsurfaces of the first and second end plate portions of the motorhousing; wherein

the first workpiece insertion recess is formed in a circular areaencompassing the first housing through hole, and in an area with apredetermined width extending in a radial direction to an externalperipheral edge of the motor housing continuously with the circular areain the external surface of the first end plate portion; and

the second workpiece insertion recess is formed in a circular areaencompassing the second housing through hole, and in an area with apredetermined width extending to an external peripheral edge of themotor housing continuously with the circular area in the externalsurface of the second end plate portion.

Here, the tool-mounting hole is preferably a hexagonal or anotherpolygonal cross section.

The maximum length in an axial direction of the rotor shaft ispreferably equal to or less than the thickness between bottom faces ofthe first and second workpiece insertion recesses in the first andsecond end plate portions on both sides of the motor housing.

Furthermore, the present invention preferably has a lead wire layingarea extending to an outside in a radial direction from an externalperipheral face of the motor housing, wherein lead wires disposed alonga recess groove formed on an inside surface of the first or second endplate portion of the motor housing are brought out to the lead wirelaying area.

The present invention also preferably has a detection mechanism fordetecting a motor magnetic pole position, wherein the detectionmechanism comprises an FG magnet disposed on one end face of the rotorshaft, and a Hall element or another magnetic sensor disposed in aninside surface area of the first or second end plate portion facing theFG magnet in the motor housing.

Effects of the Invention

In the brushless motor of the present invention, first and secondworkpiece insertion recesses are formed extending in the radialdirection on the external surface of the end plate portion on both sidesof the motor housing, and the portions on which the recesses are formedare the thinnest portions in the axial direction in the motor housing.Since the hollow portion of the rotor shaft that has a length whichallows it to be accommodated in the motor housing is used as thetool-mounting hole, the tool-mounting portion does not protrude in theaxial direction from both sides of the motor housing. The lead wirelaying area extends in the radial direction from the external peripheralface of the motor housing, and naturally does not protrude in the axialdirection from both ends of the motor housing. Since the lead wires inthe motor housing are brought out along the recess groove formed byreducing the thickness of the end plate portion of the motor housing, aspace for bringing out the lead wires does not protrude in the axialdirection from both ends of the motor housing. Additionally, a space forinstalling components for the detection mechanism is also provided inthe motor housing by using a gap between the first or second end plateportion and the end face of the rotor shaft. Therefore, in accordancewith the present invention, a hollow brushless servomotor provided witha very flat tool-mounting hole can be realized.

Hence, the brushless servomotor with the tool-mounting hole of thepresent invention is suitable for use as a machine tool that carries outpredetermined machining to facing portions of a workpiece provided withfacing portions that face each other across a narrow space as follows.That is to say, the brushless servomotor is thin and can therefore beinserted between the facing portions that face each other across thenarrow space in the workpiece. When a tool is mounted on the rotor shaftof the brushless servomotor, and in this state the facing portions ofthe workpiece are introduced along the first and second workpieceinsertion recesses from the outside toward the tool at the center in theradial direction of the motor, a tip of the facing portions can bepressed to the tool. In this state, the brushless servomotor isrotatably driven, and predetermined machining can be carried out on theworkpiece by means of the tool.

Best Mode for Carrying out the Invention

An SPM-type brushless DC servomotor according to the present inventionis described below with reference to the drawings.

FIG. 1 is a cross-sectional view along a surface containing an axis of abrushless DC servomotor in accordance with the present embodiment, FIG.2 is an end face view of the motor of FIG. 1 as seen from the directionof an arrow A, and FIG. 3 is an end face view of the motor of FIG. 1 asseen from the direction of an arrow B. A brushless DC servomotor 1 has aflattened tubular motor housing 2 sealed at both ends, and a statorassembly 3 and a rotor assembly 4 are coaxially mounted inside the motorhousing 2.

The stator assembly 3 is provided with a ring core 31 composed ofmagnetic material, and a drive coil 33 wound about a salient pole of thering core 31 via an insulator 32, and is coaxially mounted on an insideperipheral surface of a cylindrical trunk 21 of the motor housing 2. Themotor of the present example has a 20-pole, 24-slot configuration.

The rotor assembly 4 is coaxially disposed inside the stator assembly 3,and is provided with a hollow rotor shaft 41 and a ring magnet 42 fixedto a circular external peripheral surface of the rotor shaft 41, and thering magnet 42 faces the stator assembly 3 via a slight gap. The rotorshaft 41 has a cross-sectional shape provided with a internal peripheralside portion 44 in which a tool-mounting hole 43 is formed completelythrough its center, an external peripheral side portion 45 facing thestator assembly 3, and a narrow width portion 46 providing a linktherebetween, and ball bearings 47 and 48 are disposed in toroidalrecesses formed in both sides of the narrow width portion 46. An oilseal 49 is disposed on an outside of the ball bearings 47. The rotorassembly 4 is rotatably supported by the motor housing 2 by way of theball bearings 47 and 48. In the present example, the tool-mounting hole43 formed in the rotor shaft 41 is configured such that a first endplate portion 22 side is a large diameter portion 43 a, and a portion 43b on a second end plate portion 23 side has a hexagonal cross sectionwith a narrower width thereof.

As described above, the motor housing 2 has the cylindrical trunk 21 aswell as end plate portions 22 and 23 that seal both ends thereof, andcircular through holes 22 a and 23 a are formed in the center of the endplate portions 22 and 23. Both end faces 45 a and 45 b of the internalperipheral side portion 44 of the rotor shaft 41 are exposed via thecircular through holes 22 a and 23 a, respectively. First and secondworkpiece insertion recesses 24 and 25 are formed to a fixed depth incircular areas containing the circular through holes 22 a and 23 a, andin areas extending in a radial direction to an external peripheral edgeof the end plate portion continuously with the circular areas on anoutside surface of the end plate portions 22 and 23. The workpieceinsertion recesses 24 and 25 are formed by reducing the thickness of theend plate portions 22 and 23 to a fixed width. A length in an axialdirection of the rotor shaft 41 is equal to or less than the thicknessbetween bottom faces of the workpiece insertion recesses 24 and 25, andboth end faces of the rotor shaft 41 substantially match the bottomfaces of the recesses 24 and 25 in the present example.

Next, a ring-shaped FG magnet 51 is mounted on a toroidal end face 44 afacing the end plate portion 22 of the motor housing 2 in the externalperipheral side portion 45 of the rotor shaft 41. A sensor board 53 onwhich three Hall elements 52 are arranged in a circumferential directionis mounted on an inside surface of the end plate portion 22 facing theFG magnet 51. A magnetic position detection mechanism 5 is composed ofthe FG magnets 51 and Hall elements 52.

Here, a lead wire laying area 6 from the drive coil 33 and sensor board53 protrudes from an external peripheral surface of the cylindricaltrunk 21 of the motor housing 2 to an exterior in a radial direction,and has a thickness that fits within a thickness in the direction of anaxis 1 a of the motor housing 2. Also, a recess groove 26 for bringingout a lead wire is formed by reducing the thickness on an inside surfaceof the end plate portion 22 of the motor housing 2 in order to bring outlead wires from the sensor board 53.

It should be noted that the motor housing 2 of the present example has aconfiguration in which the cylindrical trunk 21 and the end plateportion 23 are integrally formed, and the end plate portion 22 isfixedly fastened to a toroidal end face of the cylindrical trunk 21.Also, a mounting flange 27 extends toward the external side in theradial direction from the external peripheral side portion of thecylindrical trunk 21, and the motor 1 is fixed to a fixed side portion(not shown) by the mounting flange 27. Furthermore, an external sideface 23 b of the end plate portion 23 is a heat-dissipating surface onwhich an uneven surface is radially provided.

Motor components are mounted in the flattened tubular motor housing 2 inthe brushless DC servomotor 1 with the above configuration, and tools(not shown) are directly mountable in the tool-mounting hole 43 of therotor shaft 41 exposed from the center through holes 22 a and 23 a ofthe end plate portions 22 and 23. Also, a portion where the thickness inthe direction of the axis 1 a is thin is formed in the motor housing 2by forming workpiece insertion recesses 24 and 25 on the outside surfaceof the two end plate portions 22 and 23 of the motor housing 2, and aworkpiece (not shown) provided with facing portions across a spacenarrower than the width of the axial direction of the motor housing 2can be introduced from the outside in the radial direction into both endportions of the tool-mounting hole 43 of the rotor shaft 41.

The end plate portion 22 of the motor housing 2 is made thinner toprovide the recess groove 26 used to bring out the lead wire, and ismade to allow the lead wire laying area 6 to fit within the thicknessdimension of the motor housing 2. Also, the magnetic position detectionmechanism 5 is disposed further inside a torque-generating portion (aportion in which the rotor assembly 4 and the stator assembly 3 faceeach other) in the radial direction, and the mechanism is configured toavoid extending the length in the axial direction of the motor.Therefore, a very flat, hollow brushless DC servomotor can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view along a surface containing an axis of abrushless DC servomotor according to the present invention;

FIG. 2 is an end face view of the motor of FIG. 1 as seen from thedirection of the arrow A; and

FIG. 3 is an end face view of the motor of FIG. 1 as seen from thedirection of the arrow B.

DESCRIPTION OF THE SYMBOLS

-   1 motor-   2 motor housing-   21 cylindrical trunk-   22, 23 end plate portion-   22 a, 23 a circular through hole-   24, 25 workpiece insertion recess-   26 recess groove for bringing out lead wire-   27 mounting flange-   3 stator assembly-   31 ring core-   33 drive coil-   4 rotor assembly-   41 rotor shaft-   42 ring magnet-   43 tool-mounting hole-   47, 48 ball bearing-   5 magnetic position detection mechanism-   51 FG magnet-   52 Hole element-   6 lead wire laying area

1. A flat, hollow brushless motor comprising: a flattened tubular motorhousing sealed at both ends, first and second housing through holesformed in a center of first and second end plate portions on both sidesof the motor housing, a rotor shaft of which a portion of both ends isexposed from the first and second housing through holes, a tool-mountinghole that extends through a center of the rotor shaft, and first andsecond workpiece insertion recesses formed in external surfaces of thefirst and second end plate portions of the motor housing, wherein thefirst and second workpiece insertion recesses are recesses of aprescribed width formed encompassing the first and second housingthrough holes, respectively, and extending to an external periphery ofthe motor housing from the housing through holes.
 2. The flat, hollowbrushless servomotor according to claim 1, wherein the tool-mountinghole has a polygonal cross section such as a hexagonal one.
 3. The flat,hollow brushless servomotor according to claim 1, wherein the maximumlength in an axial direction of the rotor shaft is equal to or less thanthe thickness between bottom faces of the first and second workpieceinsertion recesses in the first and second end plate portions on bothsides of the motor housing.
 4. The flat, hollow brushless servomotoraccording to claim 1, comprising a lead wire laying area extending to anoutside in a radial direction from an external peripheral surface of themotor housing, wherein lead wires disposed along a recess groove formedon an inside surface of the first or second end plate portion of themotor housing are brought out to the lead wire laying area.
 5. The flat,hollow brushless servomotor according to claim 1, comprising a detectionmechanism for detecting motor magnetic pole positions, wherein thedetection mechanism comprises an FG magnet disposed on one end face ofthe rotor shaft, and a magnetic sensor such as a Hall element disposedin an internal surface of the first or second end plate portion facingthe FG magnet in the motor housing.